Sofa beds of the above type are very useful pieces of furniture, being normally used as a sofa yet being readily convertible into an extra bed when needed. However, this versatility of use is obtained at a sacrifice in the seating comfort of the sofa. There have been many proposals over the years to mitigate this seating comfort problem.
In U.S. Pat. No. 3,854,153 it is proposed that the outer foot section should be formed by a transversely extending strip of heavy canvas connected by coil springs to the front member of the foldable frame. Also, diagonally arranged wires are tensioned under the wire link fabric of the body section to provide better seat cushion foundation when in the sofa position with the canvas forming the seat.
U.S. Pat. Nos. 2,634,427; 2,742,653; 2,749,653; 2,749,559, and 2,812,523 also disclose sofa beds in which a strip of material extends across the foot section to provide a seating surface when in the sofa position.
In U.S. Pat. No. 3,740,775 it is proposed to employ a flexible network in the foot section to improve seating in the sofa position.
However, all the above proposals still suffer from the disadvantage that the sofa seat will exhibit the feeling of "hammocking" whereby the sitting action of one occupant of the sofa is telegraphed to any other occupant of the sofa, and there is a tendency for the occupants to be moved together towards the middle of the sofa.
In U.S. Pat. Nos. 2,985,892 and 3,872,523 is shown the use of individual sinuous wires extending across a frame portion and which support the cushions forming the mattress when these sofas are converted to form single beds. However, these sofas do not have a foldable bed frame which unfolds and extends outwardly to form a full bed. Further, the proposals in these patents only appear to be applicable to a sofa that converts into a single bed.
Another approach to the seating discomfort problem with foldable bed frame type sofa beds has been to incorporate a separate seating surface or seat member on the frame of the bed portion, usually on the underside of the matress fabric, to improve the seating arrangement when the bed is in the closed position. Such arrangements are disclosed in U.S. Pat. Nos. 936,589; 1,058,934; 1,248,702; 1,260,600; 1,296,612; 1,306,756; 1,351,011; 1,374,661; 2,823,389; 2,851,698; and 3,317,929.
Another aspect of seating comfort with a sofa bed is the incorporation of a spring edge at the front of the seat to support and yield to movement of the underside of the thighs of the occupants seated on the sofa. It has been proposed in U.S. Pat. Nos. 2,770,814; 2,818,583 and 2,947,006 to incorporate in sofa beds spring edges along the front rail board of the sofa when in the sofa position. However, these spring edges are mounted on the foldable bed frame and move with the folding and unfolding of the bed frame. This movement of these spring edges every time the bed frame is unfolded or folded exposes them to possible damage and mechanical failure. Moreover, as the spring edge needs to fit snugly between the end arms of the sofa without any unsightly spaces, there is a tendency for the ends of the spring edge to rub against the arms, and possibly other portions of the sofa, during the folding and unfolding with eventual fabric failure due to such rubbing. There is also the risk of the side arm fabric becoming torn before failing due to the rubbing.